Coaxial circuit construction method

ABSTRACT

A coaxial circuit construction method in which a coaxial structure is fabricated by successively applying layers of metal and photopolymer material, the photopolymer layers being photographically processed to form patterns which provide the required insulation, and the metal layers being formed by upplating and precision grinding.

United States Patent Older et al. Mar. 14, 1972 [54] COAXIAL CIRCUITCONSTRUCTION 3,366,519 1/1968 Pritchard et a1. "96/362 METHOD 2,692,19010/1954 Pritkin ..96/36.2 3,042,591 7/1962 Cado ..29/625 [72] Inventors:Robert B. Older, Woodland Hills; Charles W. Smith, Canoga Park, both ofCalif. Primary Travis Brown [73] Assignee: The Buuker-Ramo Corporation,Oak Assistant Examinfl-John winkelman Brook, lll. Attorney-Frederick M.Arbuckle [22] Filed: Sept. 18, 1969 57 ABSTRACT [21] Appl.No.: 858,923 Acoaxial circuit construction method in which a coaxial structure isfabricated by successively applying layers of metal 52 U.S.Cl..96/36.2,29/625, 174/685 and P p y material,v the photopolymer layersbeing 51 int. Cl ..G03C s/oo p s p y Processed to form patterns whichprovide 58 Field of Search ..96/36.2; 29/625; 174/685 the requiredinsulation, and the metal layers being formed y up-plating and precisiongrinding. 56 R f C'ted 1 6 mm 4 Claims, 20 Drawing Figum UNITED STATESPATENTS V V. V

3,391,454 7/ 8.. r i v f A PATENTEU A 1419?? 3,649 274 SHEET 1 OF 5 ICHARLES W. SMITH BQOBERT B- OLDER Pmmwmmmz 3,649,274

' SHEET 5 [1F 5 N VN7"OR5 CHARLES 14/. SMITH ROBERT B. 0405/? A TTORNE YCOAXIAL CIRCUIT CONSTRUCTION METHOD This invention relates to a coaxialcircuit construction and method of making.

In recent years, considerable attention has been directed to improvedcoaxial circuit constructions and techniques for fabrication thereof asindicated, for example, by the constructions and techniques disclosed inUS. Pats. Nos. 3,351,702; 3,351,816; 3,35l,953;and 3,391,454.

In accordance with the objects and purposes of the present invention, acoaxial circuit construction and method of fabrication are disclosed forproviding an up-plated coaxial structure in which the requiredinsulation between the coaxial conductors is provided by a plurality ofselectively processed layers of a photopolymer material which is alsoable to serve as a satisfactory electrical insulative material betweenthe conductors. Such an approach results in an improved constructionwhich can be fabricated in a remarkably simple and inexpensive manner ascompared to presently known techniques.

The specific nature of the invention as well as other objects,advantages and uses thereof will become apparent from the followingdescription of an exemplary embodiment taken in conjunction with theaccompanying drawings in which:

FIGS. 1-20 are fragmentary pictorial and cross-sectional viewsillustrating various stages of construction in preparing coaxialcircuitry in accordance with the invention. FIGS. 2, 4, 6, 8, 10, 12 and13, and 16, and 18 and 19 are cross-sectional views taken along thecorrespondingly numbered sectioning lines indicated in the respectivepictorial views of FIGS. 1,3, 5,7, 9, l1, l4, and 17.

Like characters refer to like elements throughout the figures of thedrawings. For greater clarity, the thicknesses of various layers in thedrawings have been exaggerated. Also, for additional clarity, FIGS. 1-19of the drawings are restricted to illustrating the fabrication of only asingle coaxial conductor. However, it is to be understood that aplurality of such coaxial conductors having desired predeterminedpatterns are ordinarily batch fabricated at the same time. Accordingly,when considering FIGS. 1-19 with the description herein provided, itshould be recognized that like operations may also be simultaneouslyperformed for other coaxial conductors.

Referring to FIGS. 1 and 2, illustrated therein is a stainless steelcarrier block 10 which serves as a temporary carrier throughout thefabrication process. The block 10 is of sufficient size to include thedesired coaxial conductor circuit pattern and is also provided withregistration holes, such as illustrated by the hole 10a. A metal baselayer or foil 12, which may, for example, be copper or nickel, is bondedto the carrier block 10 preferably using jewelers wax so that thecompleted coaxial circuit structure can easily be removed to permit thecarrier block 10 to be reused.

As illustrated in FIGS. 1 and 2, a first photopolymer layer 14 isprovided over the metal base layer 12, such as by being rolled on orsolvent-bonded. It is important that the photopolymer layer 14, as wellas the other photopolymer layers provided later on in the fabricationprocess, have the dual capability of being able to be selectivelyphotographically processed as well as being able to serve as asatisfactory electrical insulative material for the resultant coaxialcircuitry. An example of a suitable photopolymer is a polyestercopolymer available from DuPont under the trademark Riston, and, whichmay be rolled on over the metal base layer 12 in FIGS. 1

and 2 to provide the photopolymer layer 14. Another example of asuitable photopolymer is Templex," also a trademarked product of DuPont.

The next step in the fabrication process is to selectively process thephotopolymer layer 14 to provide a desired photopolymer layer pattern onthe baseplate 12, such as typically illustrated by the single elongatedphotopolymer strip 14' shown in FIGS. 3 and 4. This is typicallyaccomplished by selectively exposing to light the surface of thephotopolymer layer 14 in those areas which are to be retained, and thenremoving the unexposed areas of the photopolymer layer 14 byphotographic developing.

With reference now to FIGS. 5 and 6, well-known plating techniques areemployed to up-plate the metal base layer 12 of the structure of FIGS. 3and 4 to a level to or above the su rface of the photopolymer layerpattern 14'. Precision grinding techniques employing, for example, aplanetary grinder or precision surface sander, are then used to make theresulting up-plated layer 16 flush with the surface of the photopolymerlayer pattern 14, as illustrated in FIGS. 5 and 6.

Next, a second layer of photopolymer material is provided on theresulting flush surface of the structure of FIGS. 5 and 6. Asillustrated in FIGS. 7 and 8, this second photopolymer layer isselectively exposed and developed to form a second photopolymer layerpattern 18 around the peripheral edges of the first photopolymer layerpattern 14' so as to form a recess 20 for receiving the metal materialwhich is to constitute the inner coaxial conductor of the completedcoaxial structure. This inner coaxial conductor is formed during thenext step, in which up-plating and precision grinding are again employedto provide metal layers 22 and 24 in FIGS. 9 and 10 which are flush withthe surface of the second photopolymer layer pattern 18. The flush,electrically insulated metal layer 22 within the cavity 20 constitutesthe inner coaxial conductor of the completed structure.

The next step in the fabrication process is to provide a thirdphotopolymer layer on the resulting flush surface of the structure ofFIGS. 9 and 10. As illustrated in FIGS. 11 13, this third photopolymerlayer is selectively processed to form a third photopolymer layerpattern 26 over the first and second photopolymer layer patterns 14 and18 so that photopolymer material completely encloses the metal layer 22constituting the inner coaxial conductor, except for the provision of anopening 30 at one end for feedthrough purposes. As illustrated in FIGS.14-16, up-plating and precision grinding are then once again employed toprovide metal layers 28 and 32 flush with the surface of the thirdphotopolymer layer pattern 26, the metal layer 32 serving to provideelectrical feedthrough to the inner coaxial conductor 22.

A fourth layer of photopolymer material is next provided on theresulting flush surface of the structure of FIGS. 14l6. As illustratedin FIGS. 17-19, this fourth photopolymer layer is processed to form afourth photopolymer layer pattern 34 forming an insulative ring aroundthe feedthrough metal layer 32, following which up-plating and precisiongrinding are again employed to provide metal layers 33 and 36 flush withthe fourth photopolymer layer pattern 34. It will thus be understoodthat complete conductive encirclement of the inner coaxial conductor 22will have been provided, except for the relatively small photopolymerarea provided by the fourth photopolymer layer pattern 34 insulating themetal feedthrough layer 36.

The coaxial structure of FIGS. 17-19 may be removed from the carrierplate 10 by appropriate heating. Such a planar coaxial structurecontaining a plurality of coaxial conductors fabricated as illustratedin FIGS. 1-19 could then be suitably interconnected to electricalcomponents and/or stacked with like or other planar structures invarious ways known to the art. If feedthrough connections are desired onboth sides. such may be provided by initially providing insulatedthrough-terminals in the base metal layer 12 flush with the surfacesthereof. The first photopolymer pattern would then be formed so as toprovide a small feedthrough opening over each terminal, each suchopening being filled with metal during the first up-plating operation soas to provide the desired feedthroughs.

Although the coaxial structure illustrated in FIGS. 17-19 could beremoved from the carrier plate 10 and used as a single planar coaxialstructure or stacked with other planar structures, as pointed out above,it is to be noted that additional metal and photopolymer layers could beapplied in accordance with the invention to provide a three-dimensionalstructure having a plurality of electrically interconnected levels ofcoaxial conductors, as illustrated in FIG. 20.

With reference to FIG. 20, a two-level three-dimensional coaxialstructure is illustrated having three coaxial conductors 50, 52 and 54.The coaxial conductors 50 and 52 are on the lower level and parallel toeach other, and the coaxial conductor 54 is on the upper level andperpendicular to the coaxial conductors 50 and 52. For ready comparisonand understanding, upper level elements are designated with numerals 100greater than those used for respectively corresponding lower levelelements. Also, it is to be noted that the top layer 33 of the lowerlevel is the base layer of the upper level.

FIG. 20 further illustrates how a feedthrough connection may typicallybe provided to the coaxial conductor 52 from the bottom surface of thebase layer 12. This is accomplished by the provision of an insulatedterminal 61 in the base layer 12 which is electrically connected to theinner coaxial conductor 22 via a metal layer 63 formed during the firstup-plating operation in an appropriately located opening provided in thefirst photopolymer layer pattern 14'. FIG. 20 additionally illustrateshow the inner coaxial conductor 22 of the coaxial conductor 50 may beelectrically connected, via feedthroughs 32, 36, and 163, to the innercoaxial conductor 122 of the coaxial conductor 54, and how the innercoaxial conductor 122 of the coaxial conductor 54 is in turn fed to theupper surface of the structure of FIG. 20 via feedthroughs 132 and 136.

it is to be understood that the specific forms of the inventiondescribed herein are only exemplary, and that the invention is subjectto a wide variety of possible modifications and variations infabrication, construction and use without departing from the scope ofthe invention as defined by the appended claims.

We claim 1. in a method of fabricating a shielded electrical circuitconductor, the steps of:

forming a first photopolymer layer of electrically insulative materialon a first conductive layer serving as a base layer,

photographically processing the first photopolymer layer so as to form afirst photopolymer layer pattern on said first conductive layercorresponding to a desired path for said conductor,

plating a second conductive layer on said base layer followed byprecision grinding thereof to provide an outer surface flush with theouter surface of the first photopolymer pattern,

forming a second photopolymer layer on the resulting flush surfaceformed by the flush outer surfaces of the first photopolymer layer andsecond conductive layer,

photographically processing the second photopolymer layer to form asecond photopolymer layer pattern aligned with said first photopolymerlayer pattern so as to provide an electrically isolated recess forreceiving the conductive material which is to constitute said conductor,

plating a third conductive layer on the flush second conductive layerand first photopolymer layer followed by precision grinding thereof toprovide an outer surface flush with the outer surface of the secondphotopolymer layer, the third conductive layer thus formed within saidrecess constituting said conductor,

forming a third photopolymer layer on the resulting flush surface formedby the flush outer surfaces of the second photopolymer layer and thirdconductive layer,

photographically processing the third photopolymer layer so as to form athird photopolymer layer pattern aligned with the first and secondphotopolymer layer patterns in a manner which results in the conductorbeing surrounded by photopolymer material,

plating a fourth conductive layer on the second photopolymer andconductive layers followed by precision grinding thereof to provide anouter surface flush with the outer surface of the third photopolymerlayer, and

plating a fifth conductive layer on the resulting flush surface formedby the flush outer surfaces of the third photopolymer layer and fourthconductive layer so as to thereby encircle the conductor with conductivematerial.

2. The invention in accordance with claim 1, wherein the photographicprocessing of the third photopolymer layer is such that the resultingthird photopolymer layer pattern has a feedthrough hole provided thereinextending to and exposing a portion of said conductor,

wherein said feedthrough hole is filled with conductive material whenthe fourth conductive layer is plated,

wherein prior to the plating of the fifth conductive layer a fourthphotopolymer layer is formed on the resulting flush surface formed bythe outer surfaces of the third photopolymer layer and fourth conductivelayer, said fourth photopolymer layer being photographically processedto form a fourth photopolymer layer pattern having an openingcommunicating with the opening in the third photopolymer layer pattern,and

wherein the opening in the fourth photopolymer layer pattern is platedwith conductive material when the fifth conductive layer is plated so asto thereby provide an insulated feedthrough electrical connection fromthe conductor to the outer surface of the fifth conductive layer.

3. The invention in accordance with claim 1,

wherein the steps recited are repeated using fifth conductive layer as abase layer so as to thereby form a threedimensional structure having twolevels with a conductor being formed in each level.

4. The invention in accordance with claim 3,

wherein said method includes photographically processing saidphotopolymer layers so as to form an insulated electrical connectionbetween the conductor on one level and the conductor on the other level.

2. The invention in accordance with claim 1, wherein the photographicprocessing of the third photopolymer layer is such that the resultingthird photopolymer layer pattern has a feedthrough hole provided thereinextending to and exposing a portion of said conductor, wherein saidfeedthrough hole is filled with conductive material when the fourthconductive layer is plated, wherein prior to the plating of the fifthconductive layer a fourth photopolymer layer is formed on the resultingflush surface formed by the outer surfaces of the third photopolymerlayer and fourth conductive layer, said fourth photopolymer layer beingphotographically processed to form a fourth photopolymer layer patternhaving an opening communicating with the opening in the thirdphotopolymer layer pattern, and wherein the opening in the fourthphotopolymer layer pattern is plated with conductive material when thefifth conductive layer is plated so as to thereby provide an insulatedfeedthrough electrical connection from the conductor to the outersurface of the fifth conductive layer.
 3. The invention in accordancewith claim 1, wherein the steps recited are repeated using the fifthconductive layer as a base layer so as to thereby form athree-dimensional structure having two levels with a conductor beingformed in each level.
 4. The invention in accordance with claim 3,wherein said method includes photographically processing saidphotopolymer layers so as to form an insulated electrical connectionbetween the conductor on one level and the conductor on the other level.